Why was "وَبِئْسَ الْوِرْدُ الْمَوْرُودُ" mentioned with a "و" (waw), while "بِئْسَ الرِّفْدُ الْمَرْفُودُ" was mentioned without a "و" (waw) in Surah Hud?

The Almighty's saying: ﴿الْمَوْرُودُ﴾ [Hud:98] is a circumstantial adverb (ḥāl), and the waw is for the circumstantial clause. As for the Almighty's saying: ﴿بِئْسَ الرِّفْدُ الْمَرْفُودُ﴾ [Hud:99], it is an anaphoric sentence (jumlah musta’nafah) for dispraising the curse, and the dispraised subject is omitted, indicated by the mention of the curse.